This paper describes the development and application of a procedure (The Relationship World Index) to measure the development of intimate relationships. Grounded in symbolic interaction theory, the Relationship World Index is a measure of agreement on important aspects of relationships between members of intimate dyads. The development of the measure was guided by assumptions inherent in symbolic interactionism that predict the emergence of a shared construction of reality that bonds relationship members. Research results are presented providing evidence for the reliability and validity of the measure.